The Center for Biological Diversity sent the U.S. Fish and Wildlife Service a letter Tuesday saying it would sue if the agency does not take action within 60 days.
In 2010, the center and other groups filed a petition seeking special protection for 404 species under the Endangered Species Act. The agency issued positive findings for 374 of those species, including 25 types of amphibians and reptiles. The center accuses the government of failing to take further action before an April 20, 2011 deadline.
A spokesman for the Fish and Wildlife Service did not immediately return a call seeking comment.